The present invention relates to automatic sheet metal folding machines.
Generally speaking, known types of sheet metal folding machines comprise a frame having two vertical pillars, the spacing of which defines the maximum width of sheet metal to be folded, a horizontal table fixed to the frame and adapted to support the sheet metal to be folded, a gripping member vertically displaceable for clamping the sheet metal against the table and having a leading edge for defining the folding line, and a folding member which does the actual folding. In known constructions the folding member is disposed in the front of the frame below the upper horizontal plane of the table and it is pivotable about an upper horizontal axis so that its upper edge, in contact with the sheet metal to be folded, folds the same to the desired angle. To take into account the radii of folding and the thickness of the steel metal, means are provided for adjusting the position of the pivot axis of the folding member relative to the table.
The folding of sheet metal in a known folding machine is generally carried out in the following manner:
After adjusting the pivot axis of the folding member as a function of the folding parameters, the operator places a sheet of metal so that the folding line which is marked beforehand coincides with the working edge of the table which obviously corresponds to the working edge of the gripping member. Then he lowers the gripping member to clamp the sheet metal into position and thereafter he actuates the drive mechanism for the folding member to pivot the latter to the desired angle, the folding always being carried out in a single vertical direction, i.e., downwardly.
If the sheet of metal must be folded in the opposite direction along another line, the operator must turn the sheet of metal over to bring the new folding line into coincidence with the working edge of the table and then repeat the above described steps.
Further, if the sheet of metal must be folded in the same direction, but on the opposite side and along another line, the operator must pivot the sheet horizontally through 180.degree. to reorient the new folding line to coincide with the working edge of the table before repeating the actual folding operation.
This brief description of the folding steps brings out the handling problem posed with known machines and it shows that most of the time required for folding the sheet metal is taken up by the manual displacement operations.
In French printed patent application No. 2,307,592 an automatic folding machine is disclose in which the sheet of metal is disposed in a fixed vertical position between two gripping member with horizontal leading edges pivotally mounted on the fixed frame. The machine comprises two folding members disposed symmetrically with respect to the sheet of metal and mounted on supports pivotally mounted for folding the sheet metal in one direction or the other. This arrangement avoids having to turn the sheet of metal over between two successive folding operations, but the arrangement of the gripping members pivotally mounted on the frame does not enable the sheet metal to be folded on its opposite edge. Further, the mounting of the folding members which permits considerable displacement thereof may be detrimental to accuracy especially when there are high stresses.
French printed patent application No. 2,403,126 and European printed patent application No. 0 022 22 22 teach machines for folding the edge of a sheet of metal in which the sheet metal is held in a fixed horizontal position while a single, U-shaped working member having a leading surface at the end of each one of the legs is displaceable for folding the edge of the sheet metal upwardly or downwardly. The possibilities of such a machine are limited by the dimensions of the working member, in particular the width and the depth of the U-section.